|Agroforestry In-service Training: A Training Aid for Asia & the Pacific Islands (Peace Corps, 1984)|
|Appendix D: New directions in agroforestry: The potential of tropical legume trees|
|3. Sustained outputs from legume-tree based agroforestry systems|
In addition to fuelwood, timber is needed in upland farm communities for purposes such as farmhouse construction, farm implements, and fencing. If markets exist, commercial timber for pulpwood and electric posts also may be produced by farmers.
The traditional sources of timber are the natural forests. Where these resources are no longer available, farmers may rely on forests interplanted with food crops in agroforestry farms.
In contrast with pure forest production, agroforestry farms usually produce small-sized timber. This is because (1) farmers generally want quick returns; and (2) they do not allow trees to grow older and larger to cause too much shading and reduce food crop yields. Farmers often harvest their timber crops in 4 to 10 years, depending on the rate of growth and on the desired end product.
In places where a pulp and paper plant buys timber from small farms, pulpwood can be an important wood product of agroforestry. Several species are suitable, but one legume tree that has been tried and found highly suitable, both from the user-company's viewpoint and from what farmers say about its fast rate of growth and ease in cultivating, is Albizia falcataria. On good sites and at 4-m-by-4-m spacing, it can yield from 150 to 250 m³ per hectare at age 8. Being a legume, it also improves the soil for the benefit of interplanted food crops.
Thee Establishment and Management for Timber
The initial spacing for Albizia may be four meters along the row and four meters between rows (625 trees per ha). The species has a broad crown and the canopy closes quickly, but since the leaves are small and sparse, sunlight can still reach the ground. Nevertheless, it may be necessary to change food crops over the life of the tree plantation. For instance, sun-demanding cereals like upland rice and corn may be interplanted during the first two years when tree-crown openings are still wide, then replaced by more spade-tolerant root crops like taro in the second two years as the canopy closes. The forest may be thinned at age 4 by removing every other row so that the effective spacing may then be 4 m between trees in the row and 8 m between rows.
Volume harvested through thinning could be about 30 to 60 m³ per hectare. Cereals may again be planted after thinning during the third two years, and changed to root crops once more in the last two years. Final harvest of the forest is at age 8, with a yield of around 80 to 125 m³ per hectare.
The change in the food crop from cereals to root crops before thinning and before final harvest has one additional advantage: subsurface food products are better protected from damage during harvesting operations.
As in the case of fuelwood production, it is desirable to give the farmer an opportunity to earn continuous yearly incomes from timber outputs. This could be achieved by dividing the farm into eight equal parts - or as many parts as the number of years it takes for the timber to reach harvesting age. If the farmer plants trees in one part each year, he will have one mature and harvestable pulpwood plantation each year from the ninth year onward. Because Albizia coppices and seeds well, natural regeneration is expected to be satisfactory, and continuous outputs of pulpwood and food can be expected from the agroforestry operation.
One drawback of this combination of wood-food production is that the trees are relatively far apart and may not be as effective in stabilizing the soil as the systems that allow close spacing and hedgerow planting of trees (as in food-forage production). This weakness may be minimized by intercropping trees with food crops that require less weeding and cause less soil disturbance and, therefore, less tendency for erosion.
The techniques for growing other tree species for other types of timber products needed on the farm would be basically the same as in the Albizia example, although there might be some differences in spacing and length of rotation as influenced by the growth rates of the species and the end product.